In present laser ignition applications, monolithically constructed neodymium (Nd)-doped solid-state lasers having a passive Q-switch are frequently used as the beam source. Either edge-emitting semiconductor lasers, also referred to as edge emitters, which introduce the pump light into the solid-state laser transversely or longitudinally, optionally via an optical fiber, or vertically-emitting semiconductor lasers, also referred to as VCSEL or vertical emitters, having a longitudinal pump light arrangement, as described in German Patent Application No. DE 10 2010 042 453 A1, are used as the pump light source.
Alternatively to the neodymium-doped solid-state laser, ytterbium (Yb)-doped solid-state lasers may also be used. Fiber-coupled edge emitters are used as the pump light source for ytterbium-doped solid-state lasers.
It was shown in the German Patent Application 102013202184.4 (unpublished) that for good ignition, measured on the combustion stability and the lean burning capacity of the air-gas mixture to be ignited, not only is the pulse energy in the ignition point decisive, but rather also the shape of the ignition laser beam is significant for the plasma formation and ignition of the air-gas mixture to be ignited. One measure for the shape of the ignition laser beam is beam quality M2. As a result of the smaller effective cross section in the stimulated emission of ytterbium-doped solid-state lasers in comparison to neodymium-doped solid-state lasers, ytterbium-doped solid-state lasers have a fundamentally better beam quality M2.